Metallic flavors in beers are perceived as the taste of a rusty nail, or coin-like, tinny and blood-like.
One source of these off-flavors is from aluminum pots or other non-plated steel surfaces. High iron concentrations in the brewing water can account for some of these metallic flavors in beer as well.
Check the quality of your bottle caps, filter your water if necessary or use bottled water if you must, and keep all of your grain stored under proper conditions to prevent or reduce the coin-like off-flavors in your beer.
When stainless steel is cleaned without passivation, (oxidizing the surface to produce a layer of protective oxide) the unprotected steel can also cause off flavors.
Cleaning your stainless steel pots with chlorine is the most common cause for stainless steel losing it's passivation. It attacks the chromium oxide layer and removes it thereby removing the pots protection against rust.
Using a steel scrubber on your stainless pots will also remove it’s
protective oxide layer. Once you have
lost passivation (the oxidized layer that protects stainless steel from
you will have to re-passivate your stainless steel to keep it from
To re-passivate your stainless steel, strip the pot all the way down to bare metal (ie. Clean it till it shines) with an oxalic acid based kitchen cleanser such as Bar Keeper’s Friend or Revere Ware Copper and Stainless Cleanser.
Rinse the pot well and let it dry. Leave the pot out for a few weeks in the presence of oxygen and it will re-passivate itself and cause you no more problems with metallic flavors in your homebrewed beer.
You should only have to do this once as long as you don’t clean your pots with a chlorine based cleanser or use metal scrubbies any longer.
For normal cleaning, use Powdered Brewer's Wash (PBW) which does not contain any chlorides. After you do any welding on your stainless steel brew ware, be sure to clean it well and let it air dry to re-passivate the area.
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